This invention relates to blood washing apparatus, and more particularly to blood washing apparatus in which the flow of opaque fluids through transparent tubing is detected with optical sensors. Specifically, the invention is a device that holds a transparent tube in an optical sensor, and shields the optical sensor from external light.
Blood washing is a procedure known to the art, for example, as described in U.S. Pat. No. 3,982,691 -- Centrifuge Separation and Washing Device and Method -- Charles A. Schultz issued Sept. 28, 1976. As described in the above-noted patent, human blood from volunteer donors is washed to remove unwanted constituents such as contaminants, toxicants, viruses, medicants, glycerines, cellular debris and the like, using a device based on centrifugal separation. Such a device includes a rotatable enclosure into which liquids, such as blood and wash liquids, e.g., saline solutions are injected, and from which the washed blood, wash liquids and unwanted constituents are removed. While the device described in the above-noted patent can be used to wash blood continuously, in a particular mode of operation, a predetermined amount of blood, e.g., a package available from a blood banking organization, is washed using predetermined packaged quantities of wash solution. Under such batchwise operation, wherein the apparatus is frequently started and stopped, it is imperative that the various steps in the start-up and shut-down procedure for the blood-washing apparatus be carried out with precise timing.
Apparatus for washing small batches of blood is disclosed by Herman in U.S. Pat. application Ser. No. 737,607, filed Nov. 1, 1976, now U.S. Pat. No. 4,069,968, the entire disclosure of which is incorporated herein by reference. In an embodiment of the Herman apparatus, optical sensors detect the start and finish of blood flow through transparent tubes. The sensors provide electrical signals to a control unit, which, in turn, provides signals to the various valves and pumps in the blood-washing apparatus, causing certain steps in the wash cycle to be performed at the proper times.
Optical sensors typically comprise a light emitting diode, or other source of light, and a photo transistor, or other photo-sensitive member, mounted on opposite sides of an opening. Light from the diode is sensed by the transistor. A transparent tube, through which the flow of an opaque liquid is to be detected, is placed in the opening, in the optical path between the diode and transistor. When the opaque liquid (e.g. blood) flows through the tube, the transmission of light from the diode through the optical path to the transistor is interrupted, and the transistor sends an appropriate signal to the control unit. Obviously, light from sources external to the optical sensor must be excluded, if flow of opaque fluid in the tube is to be detected.
In the blood-washing apparatus of Herman, the transparent tubing has no free ends that would fit into a hole the size of the tubing. Hence, the opening in the optical sensor must be a slot, into which a loop or bight of tubing may be inserted. The prior art method of excluding external light from the sensor was to fasten a light shield, for example, opaque tape, over the opening after the tubing has been inserted. The difficulty with this method is that the operator may forget to install the shield, causing the blood apparatus to fail to perform the right step at the right time.